In an atomic absorption spectrometer, a line emitting light source emits a light beam, which comprises the resonant spectral lines of an element being looked for. This light beam passes through a flame from a burner and impinges upon a photoelectric detector. The liquid sample, which is to be analyzed, is sprayed into the flame by means of an atomizer, so that the sample is atomized by the flame and the elements present in the sample are present in their atomic state in the flame. The attenuation of the light beam in the flame is indicative of the proportion of the element being looked for in the sample. The burner is operated with a fuel gas, such as for example acetylene, and air as the oxidizing agent. It is also known in the prior art to supply nitrous oxide gas (N.sub.2 O) as the oxidizing agent, instead of air, to the burner in order to obtain a hotter flame. Nitrous oxide has a higher proportion of oxygen than air, and when it is used, the supply of fuel gas is increased in order to provide the correct stoichiometric ratio of fuel gas and oxidizing agent.
In order to obtain reproducible conditions, a gas control device is provided, which ensures the adjustment of the gas flows to the burner, as well as the stabilization thereof.
In prior art gas control devices, needle valves were provided for the adjustment of the gas flows. The gas flows were indicated by means of a flow meter and adjusted by manual adjustment of the needle valves. In order to ensure maintenance of the gas flows once adjusted, a pressure regulator (or pressure reducer) was located upstream of each needle valve. These pressure regulators maintained constant pressure upstream of the needle valves, respectively. Thus, the gas flows were adjusted and regulated by means of adjustable restrictors at a constant inlet pressure.
Usually, the flame was first ignited with air as the oxidizing agent. The changing-over to nitrous oxide gas, if required, did not take place until after the flame was ignited. The increase in the fuel gas flow required, when operating with nitrous oxide was obtained by opening a by-pass to the needle valve.
In the prior art gas control devices, the gas flows were adjusted by hand at the needle valves. Therefore, the gas control devices had to be arranged so that the needle valves were easily accessible. This required, in many cases, relatively long conduit connections within the device.